The entire program of the Cancer Research Unit is directed towards improving the efficacy of cancer treatment through a better understanding of the biological factors involved in the response of normal and malignant tissues to treatment modalities. Cell populations of various model systems will be used. These include the intestinal epithelium, hematopoietic systems, immunological systems, several transplantable tumors-each with special characteristics (e.g., high or low growth fractions (GF), long or short cycle times, different metastatic patterns, etc.), primer dependent DNA polymerase (PDP) assay for GF measurements in exprimental and human tumors, and viral produced leukemias. Concurrently, cancer treatment regimens utilizing multi-fraction irradiation, radiation sensitizers, chemotherapeutic agents, immune stimulation, hyperthermia, and combined modality therapy will continue to be quantitatively evaluated. As the biological parameters of normal and malignant cell populations following perturbation are defined and evaluated, therapeutic ratio considerations can be applied in the planning of cancer therapy regimens.